Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The subject of the present invention is a valve
and, in particular, a valve that can be controlled to
deliver a pulsed flow of gas at its outlet.
The expression "pulsed flow" is to be
understood as meaning that this flow alternates between
a high level and a low level during predetermined
periods of time resulting from the application of a
control signal, generally in the form of square waves.
Valves which can be control_Led to make them
supply a pulsed flow at their outlet may find numerous
applications, particularly in installations for the
pulsed supply to burners of the oxyfuel type. An
installation such as this is described in particular in
document EP 524 880.
As mentioned in that document, it has in fact
been demonstrated that if a burner were to be supplied
with a pulsed flow, at least as regards either its fuel
or its oxygen supply, it would be possible to obtain a
very significant reduction in the nitrogen oxide
content of the residual flue gases from the burner. A
valve may be fitted to the fuel, particularly natural
gas, supply or to the pipe supplying the oxygen supply,
typically oxygen, or to both pipes, depending on the
installation. As is also described in the
aforementioned document, the pulsation frequency is
preferably below 1 Hz. Furthermore, i.n order to obtain
a significant effect of reducing the oxides of nitrogen
produced, it is necessary for the flow rate or pressure
of pulsed gas to have a shape as close as possible to
the square waves corresponding to the signals used to
control the valve or valves used.
Such valves can also be used for supplying
burners with air by way of a source of oxygen.
Depicted in the appended Figures 1a and lb is
one example of a control signal S for controlling the
electrically operated valve as a function of time, and
the curve of gas pressure P delivered at the outlet of
the valve receiving this control signal. Figure la
depicts the control signal S which has a first high
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level during periods T1, known as the open level, and a
low level during periods T2, known as the closed level.
The periods T1 and TZ are usually equal. Figure lb
depicts the pressure of the gas at t:he outlet of the
valve in a temporal relationship with the control
signal S. The pressure level corresponding to the
closed control signal has been labelled C and the
pressure difference between the open and closed signals
has been labelled Q. It can be seen from this figure
that during the periods corresponding to the
application of the open signal, the pressure is not
strictly in the shape of a square wave but has an
inclined rising edge F1, a falling edge F2 which is
also inclined and, while the open signal is applied,
the pressure is not constant. As has been mentioned, it
is desirable for the shape of the pressure waves to be
as rectangular as possible.
Another problem in supplying a pulsed flow lies
in the fact that these valves are used and controlled a
great many times during the period that the burner is
operating. It is therefore necessary that the valve
should not only be as near as possible to a perfect
square wave, but also for it to have very good
repeatability in terms of the opening pressure and
closure pressure of the fluid delivered over time.
In an attempt at solving this problem, a valve
described in particular in American Patent US 5 222 713
has already been proposed. The flow control element of
this valve consists of a part whose periphery is
deformable, thus making it possible, depending on the
stress applied to it, to allow the fluid to pass or to
interrupt its passage. The actuator allowing the pulsed
deformation of this component is, for example, a
piezoresistive element controlled electrically
according to the desired pulsation frequency. However,
it has become apparent that the deformation of the
element constituting the shutter element of the valve
alters with use and is not very repeatable from one
valve to another, particularly as far as the flow rates
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corresponding respectively to the open and to the
closed states are concerned.
One object of the present invention is to
provide a controllable valve, particularly for
delivering a pulsed flow, which has an outlet curve in
terms of flow or in terms of pressure which is
approximately in the form of rectangular square waves
and which, moreover, has satisfactory repeatability,
particularly as far as the flow rate or pressure
supplied in the open state and in they closed state are
concerned.
In order to achieve this objective according to
the invention, the controllable valve: particularly for
delivering a pulsed flow of fluid, comprises:
- a valve body;
- a valve seat dividing the inside of the valve
body into a fluid inlet chamber and an outlet chamber;
- a valve shutter element capable of moving in
one direction of travel to collaborate with the valve
seat;
- an actuator comprising a stationary control
part for receiving control signals and a moving part,
the said stationary part applying to the moving part a
force which corresponds to the control signal;
- first rigid means of connection extending in
the direction of travel so as to connect the said
moving part of the actuator to the said valve shutter
element;
- a mechanical stop;
- a member that can be compressed under the
effect of a force applied to it, comprising a first end
secured to the said mechanical stop; .and
- second rigid means for dynamically connecting
one of the faces of the said valve shutter element to
the second end of the said compressible member.
It will be understood that, on the one hand,
since the open and closed flow rates respectively are
defined by a rigid seat and by a rigid valve shutter
element, these flow rates are intrinsically perfectly
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stable over time. It will also be understood that, when
the control signal is no longer applied t.o the
stationary part of the actuator, the shutter element
moves in one direction or the other depending on the
embodiment in question, not only under the effect of
the cancellation of the corresponding force but also
under the effect of the release of the compressible
member which was previously compressed. It will be
understood that by using a compress_Lble member which
has properties which are very stable over time, it will
be possible to obtain very uniform valve operation.
Furthermore, it is understood that. the rising or
falling edges will be improved by comparison with the
known solutions, because of the action of the
compressible member.
According to a first embodiment, the second
rigid means of connection connect to the second end of
the compressible member that face of the valve shutter
element which faces towards the valve seat.
According to a second embodiment, the second
rigid means of connection connect to the second end of
the compressible member that face of the valve shutter
element which does not face towards the valve seat, the
said second rigid means including the said first rigid
means of connection.
It will be understood that, according to the
first embodiment, in the absence of a control signal,
the valve shutter element returns spontaneously to its
open position under the effect of the compressible
member. By contrast, in the second embodiment, the
valve shutter element returns to its closed position
under the effect of the release of the compressible
member. As will be indicated later on, the term "closed
position" must not be taken as necessarily meaning that
the shutter element is pressed against its seat in such
a way that the flow rate is effectively zero, but as
meaning a position of the shutter element such that the
flow rate supplied is low by comparison with the flow
rate supplied in the open position.
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As a preference, the compressible member
consists of a part made of elastomeric material chosen
for the consistency of its compressibility
characteristics, this part having two parallel faces
which are interposed directly or indirectly between the
mechanical stop and the shutter element.
The invention also relates to a method of
combustion in which a flow of oxidizing agent and a
flow of fuel are injected into a furnace, in which the
oxidizing agent and the fuel react with one another to
produce a flame capable of heating a charge. According
to the invention, this method is characterized in that
the flow of oxidizing agent and/or the flow of fuel is
or are injected in a pulsed manner using a pulsing
valve as described in the text of this specification.
As a preference, at least one pulsing valve is
used to inject fuel and at least one pulsing valve is
used to inject oxidizing agent, the pulsations being
identical (or different) in terms of duration but in
phase opposition. According to another alternative form
of the invention, the pulsations have the same duration
(or different durations) but are in phase.
According to another alternative form of the
invention, in which there are at least two separate
injections of oxidizing agent, using identical or
different oxidizing agents chosen from oxygen,
substantially pure oxygen, (and particularly oxygen
delivered by an apparatus for separating the gases in
the air, operating by adsorption, also known as VSA or
~~vacuum swing adsorption", particula.rly containing at
least 880 of oxygen, about 2 to 5% of argon, and any
remainder being 0 to l00 of nitrogen) oxygen-enriched
air, ai:r or oxygen-impoverished air, at least one of
the two injections being carried out using a pulsing
valve. In general, the invention also relates to the
use of a pulsing valve as defined in this specification
for pulsing an oxidizing gas and/or fuel.
Other features and advantages of the invention
will become better apparent from reading the
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description which follows of a number of embodiments of
the invention which are given by way of non-limiting
example. The description makes reference to the
appended drawings in which:
- Figures la and lb, already described, show
the control signal S and the pressure of the fluid
delivered by the valve, respectively;
- Figures 2a and 2b show, in diagrammatic form,
one first embodiment of the valve: in the closed
position and in the open position, respectively;
- Figures 3a and 3b show a skeleton diagram of
a second embodiment of the valve which is depicted in
the closed position and in the open position,
respectively;
- Figures 4a and 4b show a preferred embodiment
of the valve in greater detail in the open position and
in the closed position, respectively, and corresponding
to the principle of the valves shown in Figures 3a and
3b; and
- Figures 5a and 5b show curves expressing the
pressure of the fluid at the outlet of the valve
depicted in Figures 4a and 4b.
A first embodiment of the valve will be
described referring first of all to figures 2a <~nd 2b.
This valve consists of a valve body 10 comprising a
seat 12 which divides the inside of the valve body into
an inlet chamber 14 and an outlet chamber 16 for the
fluid. The chambers 14 and 16 are equipped respectively
with an inlet pipe 18 and with an outlet pipe 20 which
open into the lateral wall l0a of the valve body. The
valve also comprises a valve shutter element 22 capable
of moving along the axis X-X' of the valve body. This
shutter element is of course intended to collaborate
with the seat 12 to define the flow rate through the
valve according to the position of the shutter element.
The shutter element 22 is connected. by its face 22a
away from the seat 12 to an actuator 24. The actuator
24 consists of a stationary control part 26 consisting,
for example, of an induction coil powered with a
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control voltage and of a moving part 28 which, for
example, is an electromagnetic core plunger. The face
22a of the shutter element is connected to the core
plunger 28 by a rigid rod 30 which passes through the
end wall 32 of the valve body. As a preference, this
penetration is equipped with a sealing boot 34. The
core plunger 28 is extended by a second rigid rod 36,
the end 36a of which collaborates with the first end
38a of a compressible member 38. The second end 38b of
the compressible member 38 is pressed against a
mechanical stop 40.
It will be understood that the position of the
valve shutter element 22 with respects to the seat 12
and therefore the through flow rage depend on the
combination of the axial force produced by the coil 26,
applied to the core plunger 28 and re:~erenced F, and of
the compression force F' of the compressible member.
It will also be understood that the force F
applied to the core plunger 28 of course depends on the
control voltage V applied to the coil 26. E'or the
position of the shutter element corresponding to the
minimum flow rate which, as has already been explained,
is not necessarily zero, a voltage Vm is applied such
that the combination of the forces F and F' produces
the desired position of the shutter element. As a
preference, the control voltage Vm is zero. By
contrast, as Figure 2b shows, when the control voltage
VM corresponding to the open position is applied, the
resultant of the forces F and F' is such that the
shutter element 22 is moved away from its seat to
produce the maximum flow rate.
It will also be understood that, in this
embodiment, the closure of the valve, or more
specifically the arrival of the shutter element in its
minimum-flow-rate position, results not only from the
change in control voltage corresponding to the control
signal S, but also from the action of the compressible
member 38. Very quick valve closure is thus achieved.
By contrast, the opening of the valve is simply the
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result of the action of the force F applied to th.e core
plunger to compress the compressible mf~mber 38.
In the embodiment depicted in Figures 3a and
3b, we see again the valve body 10 with its upper
chamber 14 and lower chamber 16, its valve seat 12 and
its moving shutter element 22. The face 22a of the
shutter element away from the seat 12 is still
connected by a rigid rod 30 to the moving core plunger
28 of the actuator 24. The other face 22b of the
shutter element is connected to the first end 38a of
the compressible member 38 by a rigid rod 36', the
other end 38b of the compressible member 38 being
pressed against the mechanical stop 40'.
It will be understood that, in this second
embodiment, when the control voltage is equal to VM,
the shutter element 22 is brought closer to its seat 12
and the compressible member 38 is compressed. By
contrast, when the control voltage V.m is applied, the
force applied to the core plunger 28 is smaller and the
shutter element 22 moves away from the seat 12,
allowing the compressible member 38 to expand. It will
be understood that, in this embodiment, closure is
obtained simply by applying the elects romagnetic force
of the actuator, which also compresses the compressible
member 38. By contrast, valve opening is associated
both with the change in control voltage and with the
return of the compressible member 38 to its state of
rest.
The so-called open and closed positions still
result from the antagonistic effect of the force
applied to the core plunger of the actuator and of the
force developed by the compressible member. By
appropriately adjusting the force applied to the core
plunger, that is to say by appropriately adjusting the
control voltage applied to the coil 26, different open
and closed positions which will be perfectly repeatable
can thus be defined. As will be explained later on, it
is also possible to envisage for the mechanical stop 40
or 40' to be adjustable.
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In Figures 2 and 3, the compressible member 38
consists of a coil spring, the axis of compression of
which coincides with the axis of travel of the shutter
element. It is also possible, as will be explained in
greater detail later on, to use a part made of
compressible material which has a very stable and very
repeatable curve of compression a~> a function of
applied force. It will also be understood that the
choice between the two embodiments described previously
will be made on the basis of whether it is more
appropriate to have a high valve closure speed or a
high valve opening speed.
It should also be added that the actuator may
be a double-acting actuator, that is to say that the
two control voltages cause the core plunger 28 to move
in opposite directions with respect t:o the position of
rest corresponding to a zero control voltage.
One preferred embodiment of the second type of
valve depicted in Figures 3a and 3b will now be
described in greater detail with reference to Figures
4a and 4b. That figure again shows the inlet chamber
14, the outlet chamber 16 and the respective inlet pipe
18 and outlet pipe 20, occupying lateral positions with
respect to the longitudinal axis X-X' of the valve
body. The valve seat consists of a plate 50 pierced
with an orifice 52, the lateral wall 54 of which has
the shape of a cone frustum of axis X-X'. As a
preference, the half-angle a of this cone frustum, the
vertex of which points towards the outlet chamber 16,
is at least equal to 45 degrees. L_Lkewise, Figure 4a
depicts a preferred embodiment of the shutter element
of this valve, which carries the reference 56. The face
56a of the shutter element, facing tawards the seat, is
approximately flat, whereas its other face 56b also has
the overall shape of a cone frustum, the vertex of
which cone would be in the inlet chamber 14. The half-
angle b of the cone frustum forming t:he face 56b of the
shutter element is of the order of 60 degrees.
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The particular shape given to the seat 52 and
to the shutter element 56 makes it possible, on the one
hand, to stabilize the flow around the shutter element
and, on the other hand, to have a faster change in
passage cross section for the fluid between the two
chambers when the shutter element 56 is moved away from
this seat. These arrangements encourage straighter and
more upright pulsed pressure waves rising and falling
edges.
As Figures 4a and 4b show, the valve body 10 is
preferably made in two parts, an upper part 60 which
corresponds to the inlet chamber 14, and a lower part
62 corresponding to the outlet chamber 16. The seat 12
is machined in a plate 64, the periphery 64a of which
is trapped between the upper part 60 and lower part 62
of the valve body, these two parts being assembled by
any appropriate means . It is thus possible for the two
parts forming the valve body to be taken apart to
extract the plate 64 and replace it with another one in
which a seat of different dimensions has been machined.
In addition, it is envisaged for the shutter element 22
to be detached from the rod 30 such that it can be
disassembled. It is then possible for different
seat/shutter element assemblies to be fitted in the
valve to correspond to different flow rates.
In this embodiment, the position of the
mechanical stop 40' supporting the compressible member
38 is adjustable with respect to the end 42 of the
valve body. As a preference, the valve comprises a
second axial mechanical stop 44, also adjustable, which
can collaborate with a peg 46 which .is an extension of
the core plunger 28. This second mechanical stop
defines the valve wide-open position. By altering the
value of the opening voltage Vm, i.t; is possible to
define other open positions of the valve, which are of
course not as wide open as this wide-open position.
Elastomeric springs of the E:fFBE type produced
by CEF based on chloroprene or polyurethane may be used
to make the compressible member. These "springs" have a
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compression rate of 30 to 40°s. They consist of a single
ring or of two superposed rings. As they display
residual deformation, it is desirable to envisage a
fixture that allows a preload suited to this residual
deformation.
Figures 5a and 5b show the pulsed flows
obtained with the electrically operated valve described
in conjunction with Figures 4a and 4b. In these
figures, the time is shown on the abscissa axis and the
ordinate axis shows a parameter P representing the
pressure at the outlet of the valve as measured with a
pressure sensor. In the example under consideration,
the frequency is 0.5 hertz. Figure 5a shows a pressure
signal with almost vertical rising and falling edges.
In the case of Figure 5b, the square waves have rising
and falling edges which are less vertical while
remaining acceptable, but have very good consistency of
the "high" and "low" levels. The difference between
these curves is the result of the different amount of
preload applied to the elastomeric part. In the known
solutions, the control signal is of the "square wave"
type, as depicted in Figure la.
According to an alternative implementation of
the invention, it is possible to alter the shape of the
electric control signal so as to further improve the
rising and falling edges of the pressure wave at the
valve outlet. In particular, it may be envisaged for
the voltage, for a brief period of time during valve
opening, to reach a value higher than the "open" state
control value, as this further "accelerates" valve
opening. Likewise, during valve closure, it may be
envisaged for the control voltage, f_or a brief period
of time, to drop to a value below the "closed" state
control voltage value, as this accelerates valve
closure.
